This invention relates to velocity control apparatus and, more particularly, to a velocity control apparatus for a disk drive of the type comprising a recording disk rotatable about its axis, an electromagnetic read/write head for reading data from and writing data onto tracks on a surface of said disk, means coupled to the head and responsive to velocity command signals for controlling the direction and speed of movement of the head.
In the past, read-only memories (ROMS) have been employed as "look-up" tables in order to generate velocity comand signals for different distances remaining to be traveled wherein the aggregate of the velocity command signals for any particular desired distance to be traveled can be made to approximate a desired velocity vs. distance trajectory curve. If the particular system required that more than one velocity trajectory curve be generated, such as when different moving mass assemblies have to be controlled, then the output of the table ROM, after being converted to analog format, as is conventional, would have to be selectively attenuated a desired amount, such as with precision resistive networks and the like.
Examples of the above types of velocity control systems may be found in U.S. Pat. No. 3,639,754 and in U.S. Pat. No. 4,021,650.
Although these prior art systems have worked reasonably well, it would be desirable to provide an even more efficient and reliable velocity control system capable of generating velocity command signals defining any one of a plurality of velocity trajectory curves directly from the memory storage device itself, thereby avoiding the necessity of precision resistive networks and their incumbent disadvantages.